1. Field of the Invention
The present invention relates generally to medical devices for measuring grip strength, and particularly to a pinch grip dynamometer field testing calibration stand for calibrating a pinch grip dynamometer in the field without having to return the dynamometer to the factory for testing.
2. Description of the Related Art
Various portable dynamometers have been devised for determining the effects or application of loads in impact studies and medical applications, and particularly for determining grip strength, over the past few years. One of the most important problems of the conventional dynamometers is that they are lightweight and easy to move from place to place, which can cause them to become inaccurate due to mechanical jarring during transport. Also, in 1994 and 1995, the American Medical Association adopted a formula for hand injury percentage of impairment using a hand-held hand and finger grip dynamometers. Practitioners using the devices are expected to document that their use of the dynamometers is accurate. Once the dynamometer has left the manufacturing facility, it is presumed by industry, government agencies and small business consumers that necessary calibrations have been accurately determined and that the dynamometer will give correspondingly accurate comparative results in the field during the lifetime of the dynamometer.
However, testing by an independent source, such as a local Government Department of Weights and Measures, has advised that no device has been available to permit a practitioner to independently verify the accuracy of conventional dynamometers through a load bearing test as described herein. In the related art of calibration of hand grip dynamometers for measuring hand grip strength, generally the manufacturer of the hand grip dynamometer provides recalibration and other cleaning services to owners and practitioners, but this requires that owners and practitioners ship the dynamometer to the manufacture, as shown by sales pamphlets from Sammons Preston. However, this process means that the dynamometer is out of service for the periods involved in shipping and testing the instruments.
In the field of hand grip dynamometers, U.S. Pat. No. 5,945,590, issued on Aug. 31, 1999 to Theodore Becker, a co-inventor of the present invention, provides a portable and convenient stand to calibrate a hand grip dynamometer which tightly holds the hand grip of the hand grip dynamometer while applying weights to a plate that pushes down the hand grip. This '590 device provides a specialized location of load bearing that is different from the calibration stand for pinch grip dynamometers according to the present invention. The device described in the '590 patent uses a fixture shape which is unique to the hand grip dynamometer, but which is not appropriate for the pinch grip dynamometer. The '590 device, therefore, has unique stabilization location and a unique pressure location. The hand grip dynamometer has a different force receiving surface for the hand or all fingers of the hand rather than the fingers. The hand grip dynamometer has two load bearing points to be accommodated by its calibration stand, as compared to the single load bearing point of the finger grip dynamometer, which therefore requires a different calibration stand.
Other calibration devices have been developed for testing various devices. For example, U.S. Pat. No. 2,672,755, issued on February 1954 to Hohner, discloses a measuring device for forces, and more particularly, a calibrating attachment for indicating the limits of a predetermined tolerance on the scale of the measuring device. Although the mechanism for calibration is included as part of the measuring device, the test loads are applied at one end of a pivoted lever, a feature absent from the present invention.
U.S. Pat. No. 5,020,357, issued on Jun. 4, 1991 to Kovacevic et al., discloses a calibration stand for multi-force sensors which is capable of providing six components of force and moment to the sensors using support and loading apparatus on the calibration stand. Although the stand is a compact portable unit, it provides for holding the sensor in a precise position by fully permitting pitch and lateral adjustments for axial and roll or moment loading. By contrast, the portable and compact dynamometer calibration stand of the present invention does not need to provide for any lateral adjustment for axial and roll or moment loading. Also, the present invention uses simple masses or weights for calibration, whereas Kovacevic et al. uses electronic load cells.
U.S. Pat. No. 2,321,652, issued to Carliss in June, 1943, discloses a dynamometer which resembles an old-fashioned weighing machine. Weights or forces are determined by a mechanical weighing scale which is interconnected to an analog lever arm by a spring loaded mechanical linkage for indicating a force reading via a graduated scale. The mechanical linkage is quite involved, including a series of gears for transmitting various applied forces. U.S. Pat. No. 3,585,840, issued to Landsness in June, 1971, discloses a force generator which generates a force of constant amplitude and changing direction for calibrating force-sensing instruments. A resilient rod with a bearing surface provided on the free end of the rod is anchored to the instrument to be calibrated in a cantilevered arrangement. With this design, the load capacity is limited due to moments generated by the applied force and exerted on the rod. Beyond a critical applied force, failure could occur in the rod in the form of fracture, bending, etc.
U.S. Pat. No. 3,995,471, issued to Konomi et al. in December, 1976, discloses a device for calibrating a chassis dynamometer comprising a drive wheel for driving rollers of the dynamometer. The drive wheel is carried by a frame via a spring. A fluid pressure operated jack selectively lifts up the drive wheel to disengage it from rollers. U.S. Pat. No. 4,090,393, issued to Kharitonov et al. on May 1978, discloses a method and apparatus for calibrating a dynamometer wherein a force of gradual magnitudes is applied to two separate cross beams. A checking or calibrating crossbeam houses a weight which is compared to a master crossbeam upon which forces of gradual magnitudes are placed for calibration.
U.S. Pat. No. 4,798,094, issued to Newhall et al. in January, 1989 discloses an apparatus having hydrostatic bearings which provide centering of a piston and alignment of the piston-to-cylinder interface.
Several recent journal articles suggest the need in the art for reliable calibration of grip strength dynamometers, including: “Grip-Strength Measurement: A Comparison of Three Jamar Dynamometers”, Flood-Joy et al., The Occupational Therapy Journal of Research, 7:4 (1995); “The Need for Reliability and Validity in Hand Assessment Instruments”, E. E. Fess, The Journal of Hand Surgery, Vol. 11A, Number 5 (1986); “A Linear Force-summing Hand Dynamometer Independent of Point Application”, Radwin et al., Applied Ergonomics (1991); “Simultaneous Bilateral Testing: Validation of a New Protocol to Detect Insincere Effort During Strength Testing”, D. Schapmire et al., Journal of Hand Therapy (2002); “Reliability of Work Related Assessments”, Ev Innes et al., Work, Vol. 13 (1999); “A Method for Checking Jamar Dynamometer Calibration”, E. Fess, Journal of hand Therapy (1987); and “Accuracy of the Jamar Dynamometer”, Harkonen et al. (1993).
The calibration stand to field test pinch or finger grip dynamometers according to the instant invention is different from the prior and related art, in that it provides automatic calibration via load testing for a pinch grip dynamometer with reduced material elements and uncomplicated structure. This significantly improves portability of the device. No portable device or device available to the practitioner has been made for calibrating the finger or pinch grip dynamometer in the field.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a pinch grip dynamometer field testing calibration stand solving the aforementioned problems is desired.